1. Field of the Invention
The present invention relates to a communication apparatus capable of communicating with a radio terminal and radio base station and a method for identifying faults in a radio link between the radio terminal and radio base station and a computer program storage medium.
2. Related Art
Radio systems compliant with the IEEE802.11 standard have a problem that radio link errors such as radio interference occur and communication performance of radio terminals deteriorate. Therefore, in improving reliability of a radio system, when a radio link error occurs, how to speedily detect the fault which causes it, take remedial actions and shorten a time during which the communication performance deteriorates (MTTR: Mean Time To Repair) is an important issue.
Examples of the method of detecting a radio link error include a method of taking and observing statistics of the frequency of CRC errors in frames on a radio terminal or base station and thereby detecting radio interference. This is a method using a correlation between the occurrence of interference between frames on a radio link and detection of CRC errors on the radio terminal or base station, and is a method whereby when an increase is observed with respect to the frequencies at which CRC errors is detected, the occurrence of interference is estimated.
However, a CRC error is not always a phenomenon caused by only radio interference, but a phenomenon caused when, for example, communication data of a third party who has nothing to do with the other party of communication is received at a low reception level, too. Therefore, a CRC error may occur even when no radio interference occurs or when no communication is being carried out, hence there is a problem that radio interference is detected wrongly.
On the other hand, administrators need not only detect a radio link error but also identify the faults. For example, radio interference is produced by various faults such as the collision by a hidden terminal, the multipath fading caused by reflected waves due to walls or the like and non-IEEE802.11 standard interference wave such as a microwave oven and Bluetooth™. That is, even if radio interference can be detected using CRC errors, if the faults cannot be more specifically identified, the administrators cannot take specific remedial actions against the faults such as prevention of a hidden terminal or reflected wave and elimination of interference sources.
Sunggeun Jin, Sunghyun Choi, Youngsoo Kim, and Kyunghun Jang, “A Novel Idle Mode Operation in IEEE 802.11 WLANs,” IEEE 802.11-05/1263r3, January 2006 describes a method of detecting a hidden terminal. This document shows an approach of detecting a hidden terminal by observing an ACK frame from which no DATA frame can be observed, but this approach provides no measures for avoiding erroneous detection when, for example, a DATA frame is lost due to interference.
As shown above, methods of identifying the fault using statistical information have been conventionally studied, but there is a limit to the number of types of the faults that can be identified using such methods and the degree of accuracy of identification is low.